The present invention relates to devices for effecting actuation and deactuation of an electrical switch in response to changes in a sensed pressure. The invention particularly relates to pressure switches of the type employed in washing appliances where certain electrically operated appliance functions are activated in response to sensing the level of water in the appliance receptacle. Pressure switches of this type are typically employed for sensing water level in clothes washing machine tubs or in the cabinet of dishwashing machines and controlling an electrically operated waterfill valve, and the tub agitations motor.
Pressure switches employed for washing appliances typically employ a pressure responsive rubber diaphragm disposed in a housing having an inlet port communicating with a pressure chamber of which the diaphragm forms one wall. Typically a plunger is mounted on the diaphragm for actuating a snap-acting switch in the housing upon movement of the diaphragm in response to changes in pressure sensed through the inlet port. The plunger mechanism is usually pre-loaded by a bias spring; and, the pre-load is calibrated by adjustment of the spring compression to provide actuation of the snap-acting switch at a predetermined desired pressure. The calibration of the actuation pressure is generally set and sealed upon assembly of the pressure switch; and, the setting is thereafter unchanged unless provision is provided for adjustment by qualified field service personnel.
In certain types of washing appliances, it has been desired to provide for a means of changing the sensed pressure level or corresponding water level at which the electrical switch mechanism is actuated in the pressure switch without altering the original calibration setting of the switch. Such a change in switch pressure actuation or water level may be desirable where a smaller loading of articles to be washed is encountered and consequently less water is required. Additionally in washing machines employed in commercial or coin operated laundromats the proprietor or operator may wish to decrease the amount of water consumed by the machine during the washing cycle where a limted supply or shortage of water in the supply is encountered.
Additionally, it has been desired to provide a way or means of retrofitting pressure switches in existing commercial laundry machines to provide for allowing the machine operator to select as between two water levels in a quick and convenient manner without the necessity of altering the original calibration of the pressure switch.